New strategy tests for active TB stage in Asia

Part of the limitation of conventional screening lies in the use of sputum samples themselves. Children have difficulty providing a sputum sample, and so are often missed in TB screening. Also, TB can be inactive in the lungs but active in other organs and tissues. These cases too are missed by sputum screening. The two undetectable groups account for at least 20 percent of all active TB cases.

Because the antibody test relies on a blood sample, these vulnerable individuals can be picked up efficiently for the first time, said Mr Imran Khan, assistant professor in the Department of Pathology and Laboratory Medicine, and Center for Comparative Medicine at the UC Davis Medical Center. Mr Khan led development of the screening technique along with colleague Mr Paul Luciw, a professor in the same department.Preliminary studies have shown that the antibody test can detect active TB in about four out of every five cases picked up by the sputum microscopy test. It can also detect four out of five active cases that the sputum test misses. So, overall, it can identify about 80 percent of active cases compared with 50 percent for the sputum test. The initial cost of the antibody testing machines are higher than current assays, but the technology allows for so many more people to be tested, that the cost per patient would be about the same when used on a large scale, Mr Khan said.

A second diagnostic technique currently used in some South Asian clinics allows sputum samples to grow in cultures before they are examined. It offers greater sensitivity than the standard test, but because the TB bacterium grows slowly, this test can take two months.

"The fast turn-around time of the new antibody diagnostic test, in combination with high number of patients who can be tested, should enable millions of more TB patients to be screened," Mr Khan said. "As a result, effective treatment can be provided in a more timely fashion to reduce the spread of this deadly disease," he added.

The antibody test was designed to be compatible with an existing "high throughput" screening system so that it could be put to practical use quickly, Mr Khan explained. The screening instrument, developed by Luminex Corporation, is already used in other clinical lab screening settings. The TB screening system can analyze about 100 TB patient samples in two hours.